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value.go
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1397 lines (1255 loc) · 33.5 KB
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// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package constant implements Values representing untyped
// Go constants and their corresponding operations.
//
// A special Unknown value may be used when a value
// is unknown due to an error. Operations on unknown
// values produce unknown values unless specified
// otherwise.
package constant
import (
"fmt"
"go/token"
"math"
"math/big"
"math/bits"
"strconv"
"strings"
"sync"
"unicode/utf8"
)
//go:generate stringer -type Kind
// Kind specifies the kind of value represented by a Value.
type Kind int
const (
// unknown values
Unknown Kind = iota
// non-numeric values
Bool
String
// numeric values
Int
Float
Complex
)
// A Value represents the value of a Go constant.
type Value interface {
// Kind returns the value kind.
Kind() Kind
// String returns a short, quoted (human-readable) form of the value.
// For numeric values, the result may be an approximation;
// for String values the result may be a shortened string.
// Use ExactString for a string representing a value exactly.
String() string
// ExactString returns an exact, quoted (human-readable) form of the value.
// If the Value is of Kind String, use StringVal to obtain the unquoted string.
ExactString() string
// Prevent external implementations.
implementsValue()
}
// ----------------------------------------------------------------------------
// Implementations
// Maximum supported mantissa precision.
// The spec requires at least 256 bits; typical implementations use 512 bits.
const prec = 512
// TODO(gri) Consider storing "error" information in an unknownVal so clients
// can provide better error messages. For instance, if a number is
// too large (incl. infinity), that could be recorded in unknownVal.
// See also #20583 and #42695 for use cases.
// Representation of values:
//
// Values of Int and Float Kind have two different representations each: int64Val
// and intVal, and ratVal and floatVal. When possible, the "smaller", respectively
// more precise (for Floats) representation is chosen. However, once a Float value
// is represented as a floatVal, any subsequent results remain floatVals (unless
// explicitly converted); i.e., no attempt is made to convert a floatVal back into
// a ratVal. The reasoning is that all representations but floatVal are mathematically
// exact, but once that precision is lost (by moving to floatVal), moving back to
// a different representation implies a precision that's not actually there.
type (
unknownVal struct{}
boolVal bool
stringVal struct {
// Lazy value: either a string (l,r==nil) or an addition (l,r!=nil).
mu sync.Mutex
s string
l, r *stringVal
}
int64Val int64 // Int values representable as an int64
intVal struct{ val *big.Int } // Int values not representable as an int64
ratVal struct{ val *big.Rat } // Float values representable as a fraction
floatVal struct{ val *big.Float } // Float values not representable as a fraction
complexVal struct{ re, im Value }
)
func (unknownVal) Kind() Kind { return Unknown }
func (boolVal) Kind() Kind { return Bool }
func (*stringVal) Kind() Kind { return String }
func (int64Val) Kind() Kind { return Int }
func (intVal) Kind() Kind { return Int }
func (ratVal) Kind() Kind { return Float }
func (floatVal) Kind() Kind { return Float }
func (complexVal) Kind() Kind { return Complex }
func (unknownVal) String() string { return "unknown" }
func (x boolVal) String() string { return strconv.FormatBool(bool(x)) }
// String returns a possibly shortened quoted form of the String value.
func (x *stringVal) String() string {
const maxLen = 72 // a reasonable length
s := strconv.Quote(x.string())
if utf8.RuneCountInString(s) > maxLen {
// The string without the enclosing quotes is greater than maxLen-2 runes
// long. Remove the last 3 runes (including the closing '"') by keeping
// only the first maxLen-3 runes; then add "...".
i := 0
for n := 0; n < maxLen-3; n++ {
_, size := utf8.DecodeRuneInString(s[i:])
i += size
}
s = s[:i] + "..."
}
return s
}
// string constructs and returns the actual string literal value.
// If x represents an addition, then it rewrites x to be a single
// string, to speed future calls. This lazy construction avoids
// building different string values for all subpieces of a large
// concatenation. See golang.org/issue/23348.
func (x *stringVal) string() string {
x.mu.Lock()
if x.l != nil {
x.s = strings.Join(reverse(x.appendReverse(nil)), "")
x.l = nil
x.r = nil
}
s := x.s
x.mu.Unlock()
return s
}
// reverse reverses x in place and returns it.
func reverse(x []string) []string {
n := len(x)
for i := 0; i+i < n; i++ {
x[i], x[n-1-i] = x[n-1-i], x[i]
}
return x
}
// appendReverse appends to list all of x's subpieces, but in reverse,
// and returns the result. Appending the reversal allows processing
// the right side in a recursive call and the left side in a loop.
// Because a chain like a + b + c + d + e is actually represented
// as ((((a + b) + c) + d) + e), the left-side loop avoids deep recursion.
// x must be locked.
func (x *stringVal) appendReverse(list []string) []string {
y := x
for y.r != nil {
y.r.mu.Lock()
list = y.r.appendReverse(list)
y.r.mu.Unlock()
l := y.l
if y != x {
y.mu.Unlock()
}
l.mu.Lock()
y = l
}
s := y.s
if y != x {
y.mu.Unlock()
}
return append(list, s)
}
func (x int64Val) String() string { return strconv.FormatInt(int64(x), 10) }
func (x intVal) String() string { return x.val.String() }
func (x ratVal) String() string { return rtof(x).String() }
// String returns a decimal approximation of the Float value.
func (x floatVal) String() string {
f := x.val
// Don't try to convert infinities (will not terminate).
if f.IsInf() {
return f.String()
}
// Use exact fmt formatting if in float64 range (common case):
// proceed if f doesn't underflow to 0 or overflow to inf.
if x, _ := f.Float64(); f.Sign() == 0 == (x == 0) && !math.IsInf(x, 0) {
return fmt.Sprintf("%.6g", x)
}
// Out of float64 range. Do approximate manual to decimal
// conversion to avoid precise but possibly slow Float
// formatting.
// f = mant * 2**exp
var mant big.Float
exp := f.MantExp(&mant) // 0.5 <= |mant| < 1.0
// approximate float64 mantissa m and decimal exponent d
// f ~ m * 10**d
m, _ := mant.Float64() // 0.5 <= |m| < 1.0
d := float64(exp) * (math.Ln2 / math.Ln10) // log_10(2)
// adjust m for truncated (integer) decimal exponent e
e := int64(d)
m *= math.Pow(10, d-float64(e))
// ensure 1 <= |m| < 10
switch am := math.Abs(m); {
case am < 1-0.5e-6:
// The %.6g format below rounds m to 5 digits after the
// decimal point. Make sure that m*10 < 10 even after
// rounding up: m*10 + 0.5e-5 < 10 => m < 1 - 0.5e6.
m *= 10
e--
case am >= 10:
m /= 10
e++
}
return fmt.Sprintf("%.6ge%+d", m, e)
}
func (x complexVal) String() string { return fmt.Sprintf("(%s + %si)", x.re, x.im) }
func (x unknownVal) ExactString() string { return x.String() }
func (x boolVal) ExactString() string { return x.String() }
func (x *stringVal) ExactString() string { return strconv.Quote(x.string()) }
func (x int64Val) ExactString() string { return x.String() }
func (x intVal) ExactString() string { return x.String() }
func (x ratVal) ExactString() string {
r := x.val
if r.IsInt() {
return r.Num().String()
}
return r.String()
}
func (x floatVal) ExactString() string { return x.val.Text('p', 0) }
func (x complexVal) ExactString() string {
return fmt.Sprintf("(%s + %si)", x.re.ExactString(), x.im.ExactString())
}
func (unknownVal) implementsValue() {}
func (boolVal) implementsValue() {}
func (*stringVal) implementsValue() {}
func (int64Val) implementsValue() {}
func (ratVal) implementsValue() {}
func (intVal) implementsValue() {}
func (floatVal) implementsValue() {}
func (complexVal) implementsValue() {}
func newInt() *big.Int { return new(big.Int) }
func newRat() *big.Rat { return new(big.Rat) }
func newFloat() *big.Float { return new(big.Float).SetPrec(prec) }
func i64toi(x int64Val) intVal { return intVal{newInt().SetInt64(int64(x))} }
func i64tor(x int64Val) ratVal { return ratVal{newRat().SetInt64(int64(x))} }
func i64tof(x int64Val) floatVal { return floatVal{newFloat().SetInt64(int64(x))} }
func itor(x intVal) ratVal { return ratVal{newRat().SetInt(x.val)} }
func itof(x intVal) floatVal { return floatVal{newFloat().SetInt(x.val)} }
func rtof(x ratVal) floatVal { return floatVal{newFloat().SetRat(x.val)} }
func vtoc(x Value) complexVal { return complexVal{x, int64Val(0)} }
func makeInt(x *big.Int) Value {
if x.IsInt64() {
return int64Val(x.Int64())
}
return intVal{x}
}
func makeRat(x *big.Rat) Value {
a := x.Num()
b := x.Denom()
if smallInt(a) && smallInt(b) {
// ok to remain fraction
return ratVal{x}
}
// components too large => switch to float
return floatVal{newFloat().SetRat(x)}
}
var floatVal0 = floatVal{newFloat()}
func makeFloat(x *big.Float) Value {
// convert -0
if x.Sign() == 0 {
return floatVal0
}
if x.IsInf() {
return unknownVal{}
}
// No attempt is made to "go back" to ratVal, even if possible,
// to avoid providing the illusion of a mathematically exact
// representation.
return floatVal{x}
}
func makeComplex(re, im Value) Value {
if re.Kind() == Unknown || im.Kind() == Unknown {
return unknownVal{}
}
return complexVal{re, im}
}
func makeFloatFromLiteral(lit string) Value {
if f, ok := newFloat().SetString(lit); ok {
if smallFloat(f) {
// ok to use rationals
if f.Sign() == 0 {
// Issue 20228: If the float underflowed to zero, parse just "0".
// Otherwise, lit might contain a value with a large negative exponent,
// such as -6e-1886451601. As a float, that will underflow to 0,
// but it'll take forever to parse as a Rat.
lit = "0"
}
if r, ok := newRat().SetString(lit); ok {
return ratVal{r}
}
}
// otherwise use floats
return makeFloat(f)
}
return nil
}
// Permit fractions with component sizes up to maxExp
// before switching to using floating-point numbers.
const maxExp = 4 << 10
// smallInt reports whether x would lead to "reasonably"-sized fraction
// if converted to a *big.Rat.
func smallInt(x *big.Int) bool {
return x.BitLen() < maxExp
}
// smallFloat64 reports whether x would lead to "reasonably"-sized fraction
// if converted to a *big.Rat.
func smallFloat64(x float64) bool {
if math.IsInf(x, 0) {
return false
}
_, e := math.Frexp(x)
return -maxExp < e && e < maxExp
}
// smallFloat reports whether x would lead to "reasonably"-sized fraction
// if converted to a *big.Rat.
func smallFloat(x *big.Float) bool {
if x.IsInf() {
return false
}
e := x.MantExp(nil)
return -maxExp < e && e < maxExp
}
// ----------------------------------------------------------------------------
// Factories
// MakeUnknown returns the Unknown value.
func MakeUnknown() Value { return unknownVal{} }
// MakeBool returns the Bool value for b.
func MakeBool(b bool) Value { return boolVal(b) }
// MakeString returns the String value for s.
func MakeString(s string) Value { return &stringVal{s: s} }
// MakeInt64 returns the Int value for x.
func MakeInt64(x int64) Value { return int64Val(x) }
// MakeUint64 returns the Int value for x.
func MakeUint64(x uint64) Value {
if x < 1<<63 {
return int64Val(int64(x))
}
return intVal{newInt().SetUint64(x)}
}
// MakeFloat64 returns the Float value for x.
// If x is -0.0, the result is 0.0.
// If x is not finite, the result is an Unknown.
func MakeFloat64(x float64) Value {
if math.IsInf(x, 0) || math.IsNaN(x) {
return unknownVal{}
}
if smallFloat64(x) {
return ratVal{newRat().SetFloat64(x + 0)} // convert -0 to 0
}
return floatVal{newFloat().SetFloat64(x + 0)}
}
// MakeFromLiteral returns the corresponding integer, floating-point,
// imaginary, character, or string value for a Go literal string. The
// tok value must be one of token.INT, token.FLOAT, token.IMAG,
// token.CHAR, or token.STRING. The final argument must be zero.
// If the literal string syntax is invalid, the result is an Unknown.
func MakeFromLiteral(lit string, tok token.Token, zero uint) Value {
if zero != 0 {
panic("MakeFromLiteral called with non-zero last argument")
}
switch tok {
case token.INT:
if x, err := strconv.ParseInt(lit, 0, 64); err == nil {
return int64Val(x)
}
if x, ok := newInt().SetString(lit, 0); ok {
return intVal{x}
}
case token.FLOAT:
if x := makeFloatFromLiteral(lit); x != nil {
return x
}
case token.IMAG:
if n := len(lit); n > 0 && lit[n-1] == 'i' {
if im := makeFloatFromLiteral(lit[:n-1]); im != nil {
return makeComplex(int64Val(0), im)
}
}
case token.CHAR:
if n := len(lit); n >= 2 {
if code, _, _, err := strconv.UnquoteChar(lit[1:n-1], '\''); err == nil {
return MakeInt64(int64(code))
}
}
case token.STRING:
if s, err := strconv.Unquote(lit); err == nil {
return MakeString(s)
}
default:
panic(fmt.Sprintf("%v is not a valid token", tok))
}
return unknownVal{}
}
// ----------------------------------------------------------------------------
// Accessors
//
// For unknown arguments the result is the zero value for the respective
// accessor type, except for Sign, where the result is 1.
// BoolVal returns the Go boolean value of x, which must be a Bool or an Unknown.
// If x is Unknown, the result is false.
func BoolVal(x Value) bool {
switch x := x.(type) {
case boolVal:
return bool(x)
case unknownVal:
return false
default:
panic(fmt.Sprintf("%v not a Bool", x))
}
}
// StringVal returns the Go string value of x, which must be a String or an Unknown.
// If x is Unknown, the result is "".
func StringVal(x Value) string {
switch x := x.(type) {
case *stringVal:
return x.string()
case unknownVal:
return ""
default:
panic(fmt.Sprintf("%v not a String", x))
}
}
// Int64Val returns the Go int64 value of x and whether the result is exact;
// x must be an Int or an Unknown. If the result is not exact, its value is undefined.
// If x is Unknown, the result is (0, false).
func Int64Val(x Value) (int64, bool) {
switch x := x.(type) {
case int64Val:
return int64(x), true
case intVal:
return x.val.Int64(), false // not an int64Val and thus not exact
case unknownVal:
return 0, false
default:
panic(fmt.Sprintf("%v not an Int", x))
}
}
// Uint64Val returns the Go uint64 value of x and whether the result is exact;
// x must be an Int or an Unknown. If the result is not exact, its value is undefined.
// If x is Unknown, the result is (0, false).
func Uint64Val(x Value) (uint64, bool) {
switch x := x.(type) {
case int64Val:
return uint64(x), x >= 0
case intVal:
return x.val.Uint64(), x.val.IsUint64()
case unknownVal:
return 0, false
default:
panic(fmt.Sprintf("%v not an Int", x))
}
}
// Float32Val is like Float64Val but for float32 instead of float64.
func Float32Val(x Value) (float32, bool) {
switch x := x.(type) {
case int64Val:
f := float32(x)
return f, int64Val(f) == x
case intVal:
f, acc := newFloat().SetInt(x.val).Float32()
return f, acc == big.Exact
case ratVal:
return x.val.Float32()
case floatVal:
f, acc := x.val.Float32()
return f, acc == big.Exact
case unknownVal:
return 0, false
default:
panic(fmt.Sprintf("%v not a Float", x))
}
}
// Float64Val returns the nearest Go float64 value of x and whether the result is exact;
// x must be numeric or an Unknown, but not Complex. For values too small (too close to 0)
// to represent as float64, Float64Val silently underflows to 0. The result sign always
// matches the sign of x, even for 0.
// If x is Unknown, the result is (0, false).
func Float64Val(x Value) (float64, bool) {
switch x := x.(type) {
case int64Val:
f := float64(int64(x))
return f, int64Val(f) == x
case intVal:
f, acc := newFloat().SetInt(x.val).Float64()
return f, acc == big.Exact
case ratVal:
return x.val.Float64()
case floatVal:
f, acc := x.val.Float64()
return f, acc == big.Exact
case unknownVal:
return 0, false
default:
panic(fmt.Sprintf("%v not a Float", x))
}
}
// Val returns the underlying value for a given constant. Since it returns an
// interface, it is up to the caller to type assert the result to the expected
// type. The possible dynamic return types are:
//
// x Kind type of result
// -----------------------------------------
// Bool bool
// String string
// Int int64 or *big.Int
// Float *big.Float or *big.Rat
// everything else nil
func Val(x Value) any {
switch x := x.(type) {
case boolVal:
return bool(x)
case *stringVal:
return x.string()
case int64Val:
return int64(x)
case intVal:
return x.val
case ratVal:
return x.val
case floatVal:
return x.val
default:
return nil
}
}
// Make returns the Value for x.
//
// type of x result Kind
// ----------------------------
// bool Bool
// string String
// int64 Int
// *big.Int Int
// *big.Float Float
// *big.Rat Float
// anything else Unknown
func Make(x any) Value {
switch x := x.(type) {
case bool:
return boolVal(x)
case string:
return &stringVal{s: x}
case int64:
return int64Val(x)
case *big.Int:
return makeInt(x)
case *big.Rat:
return makeRat(x)
case *big.Float:
return makeFloat(x)
default:
return unknownVal{}
}
}
// BitLen returns the number of bits required to represent
// the absolute value x in binary representation; x must be an Int or an Unknown.
// If x is Unknown, the result is 0.
func BitLen(x Value) int {
switch x := x.(type) {
case int64Val:
u := uint64(x)
if x < 0 {
u = uint64(-x)
}
return 64 - bits.LeadingZeros64(u)
case intVal:
return x.val.BitLen()
case unknownVal:
return 0
default:
panic(fmt.Sprintf("%v not an Int", x))
}
}
// Sign returns -1, 0, or 1 depending on whether x < 0, x == 0, or x > 0;
// x must be numeric or Unknown. For complex values x, the sign is 0 if x == 0,
// otherwise it is != 0. If x is Unknown, the result is 1.
func Sign(x Value) int {
switch x := x.(type) {
case int64Val:
switch {
case x < 0:
return -1
case x > 0:
return 1
}
return 0
case intVal:
return x.val.Sign()
case ratVal:
return x.val.Sign()
case floatVal:
return x.val.Sign()
case complexVal:
return Sign(x.re) | Sign(x.im)
case unknownVal:
return 1 // avoid spurious division by zero errors
default:
panic(fmt.Sprintf("%v not numeric", x))
}
}
// ----------------------------------------------------------------------------
// Support for assembling/disassembling numeric values
const (
// Compute the size of a Word in bytes.
_m = ^big.Word(0)
_log = _m>>8&1 + _m>>16&1 + _m>>32&1
wordSize = 1 << _log
)
// Bytes returns the bytes for the absolute value of x in little-
// endian binary representation; x must be an Int.
func Bytes(x Value) []byte {
var t intVal
switch x := x.(type) {
case int64Val:
t = i64toi(x)
case intVal:
t = x
default:
panic(fmt.Sprintf("%v not an Int", x))
}
words := t.val.Bits()
bytes := make([]byte, len(words)*wordSize)
i := 0
for _, w := range words {
for j := 0; j < wordSize; j++ {
bytes[i] = byte(w)
w >>= 8
i++
}
}
// remove leading 0's
for i > 0 && bytes[i-1] == 0 {
i--
}
return bytes[:i]
}
// MakeFromBytes returns the Int value given the bytes of its little-endian
// binary representation. An empty byte slice argument represents 0.
func MakeFromBytes(bytes []byte) Value {
words := make([]big.Word, (len(bytes)+(wordSize-1))/wordSize)
i := 0
var w big.Word
var s uint
for _, b := range bytes {
w |= big.Word(b) << s
if s += 8; s == wordSize*8 {
words[i] = w
i++
w = 0
s = 0
}
}
// store last word
if i < len(words) {
words[i] = w
i++
}
// remove leading 0's
for i > 0 && words[i-1] == 0 {
i--
}
return makeInt(newInt().SetBits(words[:i]))
}
// Num returns the numerator of x; x must be Int, Float, or Unknown.
// If x is Unknown, or if it is too large or small to represent as a
// fraction, the result is Unknown. Otherwise the result is an Int
// with the same sign as x.
func Num(x Value) Value {
switch x := x.(type) {
case int64Val, intVal:
return x
case ratVal:
return makeInt(x.val.Num())
case floatVal:
if smallFloat(x.val) {
r, _ := x.val.Rat(nil)
return makeInt(r.Num())
}
case unknownVal:
break
default:
panic(fmt.Sprintf("%v not Int or Float", x))
}
return unknownVal{}
}
// Denom returns the denominator of x; x must be Int, Float, or Unknown.
// If x is Unknown, or if it is too large or small to represent as a
// fraction, the result is Unknown. Otherwise the result is an Int >= 1.
func Denom(x Value) Value {
switch x := x.(type) {
case int64Val, intVal:
return int64Val(1)
case ratVal:
return makeInt(x.val.Denom())
case floatVal:
if smallFloat(x.val) {
r, _ := x.val.Rat(nil)
return makeInt(r.Denom())
}
case unknownVal:
break
default:
panic(fmt.Sprintf("%v not Int or Float", x))
}
return unknownVal{}
}
// MakeImag returns the Complex value x*i;
// x must be Int, Float, or Unknown.
// If x is Unknown, the result is Unknown.
func MakeImag(x Value) Value {
switch x.(type) {
case unknownVal:
return x
case int64Val, intVal, ratVal, floatVal:
return makeComplex(int64Val(0), x)
default:
panic(fmt.Sprintf("%v not Int or Float", x))
}
}
// Real returns the real part of x, which must be a numeric or unknown value.
// If x is Unknown, the result is Unknown.
func Real(x Value) Value {
switch x := x.(type) {
case unknownVal, int64Val, intVal, ratVal, floatVal:
return x
case complexVal:
return x.re
default:
panic(fmt.Sprintf("%v not numeric", x))
}
}
// Imag returns the imaginary part of x, which must be a numeric or unknown value.
// If x is Unknown, the result is Unknown.
func Imag(x Value) Value {
switch x := x.(type) {
case unknownVal:
return x
case int64Val, intVal, ratVal, floatVal:
return int64Val(0)
case complexVal:
return x.im
default:
panic(fmt.Sprintf("%v not numeric", x))
}
}
// ----------------------------------------------------------------------------
// Numeric conversions
// ToInt converts x to an Int value if x is representable as an Int.
// Otherwise it returns an Unknown.
func ToInt(x Value) Value {
switch x := x.(type) {
case int64Val, intVal:
return x
case ratVal:
if x.val.IsInt() {
return makeInt(x.val.Num())
}
case floatVal:
// avoid creation of huge integers
// (Existing tests require permitting exponents of at least 1024;
// allow any value that would also be permissible as a fraction.)
if smallFloat(x.val) {
i := newInt()
if _, acc := x.val.Int(i); acc == big.Exact {
return makeInt(i)
}
// If we can get an integer by rounding up or down,
// assume x is not an integer because of rounding
// errors in prior computations.
const delta = 4 // a small number of bits > 0
var t big.Float
t.SetPrec(prec - delta)
// try rounding down a little
t.SetMode(big.ToZero)
t.Set(x.val)
if _, acc := t.Int(i); acc == big.Exact {
return makeInt(i)
}
// try rounding up a little
t.SetMode(big.AwayFromZero)
t.Set(x.val)
if _, acc := t.Int(i); acc == big.Exact {
return makeInt(i)
}
}
case complexVal:
if re := ToFloat(x); re.Kind() == Float {
return ToInt(re)
}
}
return unknownVal{}
}
// ToFloat converts x to a Float value if x is representable as a Float.
// Otherwise it returns an Unknown.
func ToFloat(x Value) Value {
switch x := x.(type) {
case int64Val:
return i64tor(x) // x is always a small int
case intVal:
if smallInt(x.val) {
return itor(x)
}
return itof(x)
case ratVal, floatVal:
return x
case complexVal:
if Sign(x.im) == 0 {
return ToFloat(x.re)
}
}
return unknownVal{}
}
// ToComplex converts x to a Complex value if x is representable as a Complex.
// Otherwise it returns an Unknown.
func ToComplex(x Value) Value {
switch x := x.(type) {
case int64Val, intVal, ratVal, floatVal:
return vtoc(x)
case complexVal:
return x
}
return unknownVal{}
}
// ----------------------------------------------------------------------------
// Operations
// is32bit reports whether x can be represented using 32 bits.
func is32bit(x int64) bool {
const s = 32
return -1<<(s-1) <= x && x <= 1<<(s-1)-1
}
// is63bit reports whether x can be represented using 63 bits.
func is63bit(x int64) bool {
const s = 63
return -1<<(s-1) <= x && x <= 1<<(s-1)-1
}
// UnaryOp returns the result of the unary expression op y.
// The operation must be defined for the operand.
// If prec > 0 it specifies the ^ (xor) result size in bits.
// If y is Unknown, the result is Unknown.
func UnaryOp(op token.Token, y Value, prec uint) Value {
switch op {
case token.ADD:
switch y.(type) {
case unknownVal, int64Val, intVal, ratVal, floatVal, complexVal:
return y
}
case token.SUB:
switch y := y.(type) {
case unknownVal:
return y
case int64Val:
if z := -y; z != y {
return z // no overflow
}
return makeInt(newInt().Neg(big.NewInt(int64(y))))
case intVal:
return makeInt(newInt().Neg(y.val))
case ratVal:
return makeRat(newRat().Neg(y.val))
case floatVal:
return makeFloat(newFloat().Neg(y.val))
case complexVal:
re := UnaryOp(token.SUB, y.re, 0)
im := UnaryOp(token.SUB, y.im, 0)
return makeComplex(re, im)
}
case token.XOR:
z := newInt()
switch y := y.(type) {
case unknownVal:
return y
case int64Val:
z.Not(big.NewInt(int64(y)))
case intVal:
z.Not(y.val)
default:
goto Error
}
// For unsigned types, the result will be negative and
// thus "too large": We must limit the result precision
// to the type's precision.
if prec > 0 {
z.AndNot(z, newInt().Lsh(big.NewInt(-1), prec)) // z &^= (-1)<<prec
}
return makeInt(z)
case token.NOT:
switch y := y.(type) {
case unknownVal:
return y
case boolVal:
return !y
}